Dental calculus from 58 medieval and post-medieval skeletons from Vitoria, Spain and a single Alaskan Inuit skeleton were tested for stable carbon and nitrogen isotopes. There are several sources of carbon and nitrogen in calculus, including oral mucosa, saliva, food particles, and oral bacteria. There was sufficient carbon and nitrogen to obtain consistent δ13C and δ15N values. Results were replicable and comparable to European values based on bone collagen, with means of -21.2 for δ13C and +11.8 for δ15N. The single Alaskan Inuit yielded a δ15N value of +17.5‰, consistent with data on modern Greenlandic Inuit consuming a diet rich in marine food. Calculus is a secondary biomaterial that is not an integral part of the dental or skeletal system. As such, dental calculus may provide a new avenue for paleodietary research where the use of primary biomaterials is precluded.